1. Field of The Invention
The present invention relates to a safety belt arrangement, such as a safety belt arrangement for use in an automobile or other vehicle.
2. Background Art
A previously proposed safety belt arrangement incorporates a reel comprising a rotable spindle upon which the belt is wound. The spindle is spring biassed to wind in the belt. The reel also incorporates a locking arrangement to lock the spindle in response to the sensing of predetermined conditions such as a rate of vehicle deceleration in excess of a predetermined rate or the paying out of the belt from the reel at a rate in excess of a predetermined rate. Thus, for example, if an accident occurs in which a vehicle is subjected to an impact and thus decelerates at a very high rate, the spindle will be locked. In such a situation the occupants of the vehicle will continue to move forwardly within the vehicle as a result of the momentum which they possess immediately before the accident. A very large force will then be exerted upon the belt by its wearer, this force tending to extract the belt from the reel. This force exerted on the belt causes the portion of the belt which is wound upon the spindle to tighten around the stationary spindle, which in turn causes a further, short length of belt to be paid out.
The paying out of this further length of belt is particularly undesirable, since this enbables the wearer of the safety belt to move further forward within the vehicle before being restrained by the belt. In an accident situation it is desirable for the seat belt to restrain the occupant as quickly as possible, so as to prevent forward movement of the occupant towards the dashboard or windshield of the vehicle. In addition, when a large force is placed upon the belt by its wearer, the belt will stretch by a certain proportion and clearly the amount by which the belt stretches will be greater, if a greater length of belt is paid out from the reel. The paying out of a further length of belt from the reel, once the spindle has been locked is sometimes referred to as the "film spool effect".
The film spool effect may be partially overcome by using a web lock, this being a locking arrangement which serves to clamp the belt web itself in order to prevent the paying out of an further length of belt from the reel once the spindle has been locked. Various web lock designs have been proposed previously and examples are shown in British Patent Documents GB2168593A, GB-2177891A and French Patent Document FR2511320C.
The web locks described in these various prior art documents utilise the force present in the belt web to move the web lock into engagement with the belt. This prevents any further length of belt from being paid out. The web lock must open again, so as to release the belt web once the force in the web has dropped to a level below a predetermined level. It has been proposed that the web lock may be actuated so as to lock the belt web whenever the spindle locking arrangement is actuated, but this results in significant, unnecessary wear of the belt web. British Patent document GB 2113978A discloses a web lock which is adapted to be actuated only in response to movement of the retractor reel. The retractor reel is slidably mounted in position, but is biassed to a lower position by means of a spring. The described arrangement is such that when the spindle of the retractor reel is locked, due, for example, to deceleration of the vehicle, any tension applied to the safety belt will tend to move the retractor reel upwardly, against the biassing effect of the spring. This upward movement of the retractor reel causes a clamping member to firmly clamp the belt web in the region where the web leaves the retractor reel. However, a disadvantage of this arrangement is that if an extremely high force is applied to the safety belt, by the weight of the person restrained by the safety belt being thrown forwardly, there is no "give" at all in the system, and the person restrained by the safety belt can actually be injured by the safety belt. The present invention seeks to avoid this particular difficulty.